1. Field of the Invention
The present invention relates to an antenna device, and more specifically to an antenna device used for extremely high frequency (EHF) wireless LANs.
2. Description of the Related Art
Non-directional antenna devices have generally been used for wireless LANs. The non-directional antenna device allows the users at any positions in a predetermined coverage to access a wireless LAN. The antenna device is located on the center or at a specific corner in the area of the predetermined coverage of the wireless LAN. The users in the predetermined coverage can accordingly access the wireless LAN without giving special attention to the position of the antenna device.
In the application of a wireless LAN between multiple different buildings, for example, two buildings, access points for the wireless LAN are respectively set in the two buildings. Directional antenna devices having high directional characteristic are located to face each other in the two different buildings and are linked to respective access points for the connection of the wireless LAN. This layout extends the coverage of the respective antenna devices, while restricting accesses from unauthorized devices.
The directional antenna device and the non-directional antenna device for the wireless LANs are completely different and separate systems, and either the directional antenna device or the non-directional antenna device is selected according to the applications. Some change of the settings at an access point may thus require replacement of the whole antenna device.
The directional antenna and the non-directional antenna have substantially opposite directional characteristics and dot not satisfy a demand for a certain level of directional characteristic, which is lower than the directional characteristic of the directional antenna. Such requirements are often found when the access point is located at the corner of a room or a building. Application of a non-directional antenna to the demand may cause an insufficient coverage and allow illegal accesses from outside the room or the building.